2. Why is the fossil record incomplete?
It takes the right conditions at the right time in the
right place.
- some organisms are simply not likely to yield fossils
- sedimentation does not occur in all habitats
- fossils must survive geological events and weather the elements for millions of years before discovery

3. Process of Fossilization
After remains are buried by sediments:
Compression/impression/casts/molds:impressions or casts
made before decomposition (like footprints).
(2) Permineralized fossils: precipitation of minerals in
cells before decomposition.
Or Occasionally:
(1) Unaltered remains: Frozen , amber embedded, peat bogs.

4. permineralized fossils
amber
cast
Impression fossil

5. Fossil Record is Biased
Fossilization is higher for organisms that are:
Durable and likely to be buried in an
anoxic environment (low land or marine habitats)
Also, there is temporal and geographic bias:
Probability that an organism will be fossilized depends
on the geographical area and historical time.

6. Fossils and associated rocks contain
Radiometric Dating
Fossils and associated rocks contain
reactive elements that decay at known rates
Half-life
Uranium235 --> Lead = 7 x 108 years
Carbon > Nitrogen = 5730 years
Parent Atom
Daughter Atom

7. Radioisotope Decay Time (half-lives) 1 2 3 Surviving Parent Atoms
Accumulating
Daughter
Atoms 1 2 3
1/1
1/3
1/7
1. Find fossil
2. Determine ratio of parent
to daughter atoms
3. Determine number of
elapsed half-lives
4. Estimate age of fossil

8. Try this problem
You are using C14 (half-life = years) radioisotope dating to determine the age of rocks associated with a fossil. The percentage of daughter isotope atoms (N14)) is 87.5%. What is the age of the fossil?
17,190 yrs

9. There are Good Examples of Macroevolution
in the Fossil Record
Sarcopterygii --> Ichthyostega --> Amphibia
see also (Figure 4.6)
Gradualism : (e.g. limbs are intermediate)
Mosaic evolution:
(limbs evolved
faster than braincase, tail fin, tooth structure

10. Other Examples From Book To Review (Chapter 4)
Origin of Birds
Archaeopteryx is but one of many fossils
Origin of Mammals
- Gradual evolution of “reptilian” skull and jaw
Origin of Cetacea
A series of fossils have recently been discovered showing adaptation to aquatic life
Origin of Hominins
We are the lone survivors of an otherwise
extinct radiation of bipedal African hominids

11. Vertebrates Hair Mammary Glands Amniotic Egg Endothermy Four Limbs
Cartilagenous
Fish
Hagfish,
Lampreys
Bony
Fish
Amphibians
Mammals
Birds
Reptiles
Hair
Mammary Glands
Amniotic Egg
Endothermy
Four Limbs
Terrestrial Phase
Bony Skeleton
Swim Bladder
Skull
Backbone
Paired Fins
Jaws

12. Mammals Hair, mammary glands Most advanced nervous system
Learning important to
survival
Warm blooded
Humans are mammals

13. Humans are primate mammals
Class Mammalia
Order Primates
Prosimians (e.g. lemurs)
Tarsiers
Anthropoids (e.g. monkeys, hominoids)

14. Lemur
Tarsier
Macaque

15. Primates : Humble Beginning
Rabbit
Shrew
Shrew-like
Ancestor

16. Homininae : African Great Apes
Major Primate Groups
Family Hominidae
Old World
Monkeys
Orangutan
Chimp
Human
Tarsiiformes
Gibbons
Gorilla
Lemurs
New World
Monkeys
Homininae : African Great Apes
and Humans
Hominidea : Great Apes and Humans
Hominoidea : Apes and Humans

17. What Features Are Associated With Primate Evolution?
I. Sensory Adaptations
Protected, forward looking eyes with stereoscopic vision
Improved sight : more detail even in low light
Reduction of olfactory structures

18. What Features Are Associated With Primate Evolution?
II. Adaptations for tree-climbing and insectivory
Freely moving limbs and digits
Long mobile digits capable of grasping
Retention of tail as organ of balance
Evolution of upright body posture and extensive head rotation
Increased body size
Evolution of nervous system to give precise and rapid control of movement

19. Major Primate Groups Hasegawa et al. 1987 Orangutan Chimp Human
Family Hominidae
Old World
Monkeys
Orangutan
Chimp
Human
Tarsiiformes
Gibbons
Gorilla
Lemurs
New World
Monkeys
25 mya
12 mya
6 mya
Hasegawa et al. 1987
5 mya
38 mya
Estimated
Divergence Times

20. What Traits Do Humans and Apes Share?
Larger Brain
Absence of a tail
More erect posture
Greater flexibility of hips, ankles, wrist, thumb
DNA sequence similarity

21. Gorilla Chimpanzee Human
Horai et al (1995) Proc. Nat Acad Sci. 92:
Mito DNA (complete sequences)
Kim and Takenaka (1996) A. J. Phys. Anth. 100:
Y-chromosome DNA
Ruvolo (1997) Mol Biol Evol 10:
Examined 14 different DNA data sets
Satta et al (2000) Mol. Phyl. Evol 14:
Autosomal DNA (45 genes, 47,000 bp of DNA)
Paabo (2003) Nature 421:
Review of human and chimp/ape genomes.

22. Common Ancestor of Chimp/Human
Knuckle-walker?
Broad-fruit based diet
May have hunted
May have used tools
May have had complex social relationships:
(e.g.warfare, cannabalism, sharing,
teaching, compassion)

23. Our Understanding of Human Evolution is Primarily Based on Fossils